1. Field of the Invention
The present invention relates to a perpendicular magnetic recording head and a magnetic disc apparatus using the perpendicular magnetic recording head.
2. Description of the Related Art
A conventional magnetic disc apparatus of a perpendicular recording system has a double layered perpendicular magnetic recording medium comprising a soft magnetic underlayer made of a high permeability material and a perpendicular recording layer having a magnetic anisotropy in the direction perpendicular to the film plane thereof, which are formed on a disc substrate, and a single-pole recording head including a main pole and an auxiliary pole each made of a high permeability material. The auxiliary pole serves to efficiently conduct a magnetic flux during a recording operation.
When the conventional magnetic disc apparatus of a perpendicular recording system is required to achieve a higher recording density, a serious problem is generated that signals recorded in the recording medium previously are deteriorated or erased by a weak magnetic field leaked from the auxiliary pole during a recording operation.
Incidentally, U.S. Pat. No. 4,873,599 discloses a technique that uses an auxiliary pole whose permeability progressively increases from each edge to the center thereof in the moving direction of the head, in order to overcome the increase in pulse noise generation in the edge of the auxiliary pole. In this technique, however, it is impossible to basically overcome the above-noted problem of the deterioration and erasure of the signals already recorded in the recording medium.
Also, since the conventional single-pole recording head has high sensitivity to a disturbance magnetic field, it is possible that the disturbance magnetic field brings about deterioration and erasure of previously recorded information. Thus, a structure that a write shield is arranged on the trailing side to the single-pole recording head is proposed to suppress penetration of the disturbance magnetic field (see U.S. Pat. No. 5,311,387). The particular structure makes it possible to prevent the signal deterioration in a region right under the main pole. However, the structure gives rise to a problem that a magnetic field generated from the main pole during a recording operation is introduced into the write shield to cause a weak leakage field from the write shield, which deteriorates or erases the previously recorded signals.